I like the rough/hand drawn look; it reminds me of a certain artist, whose name eludes me (actually, I think I don't know it at all--I just know his/her work).
If you colour it, definitely go with something very light--watercolours seem to be the wisest choice. Definitely don't go for a cleaned-up, typical computer-generated look--it'll rob the design of its spirit.
You might also, if you're -very- good, turn it into an Alphonse Mucha, art nouveau sort of thing--it seems to kinda sorta have that feel to me, for some reason.